ACL injury has been shown to have long-lasting and severe consequences on the different structures of the knee such as the articular cartilage and meniscus. Cartilage thickness changes in particular are indicative of osteoarthritic changes in the tibiofemoral joint. While there has been significant research focused on cartilage changes of the tibia and femur following severe joint trauma, there has been little work focused on patellar cartilage. The following goals were set forth for this study. First, to establish a robust coordinate system to accurately determine the location and orientation of the patella relative to the femur and establish the distribution of articular cartilage thickness on the patella. Second, to determine the effects of ACL injury on patellar cartilage thickness. Twenty-one individuals (10 males, 11 females) were studied. All individuals had suffered their first ACL injury. MRI data from both the healthy and injured knees were collected an average of 4 ± 0.9 years following the initial injury and ACL reconstruction surgery. Using MRI data, the bone and cartilage surfaces were manually segmented and imported into MATLAB for study. The difference in cartilage thickness between the healthy and injured knees within individuals was the primary measure of analysis. Analysis revealed both decreases and increases in cartilage thickness of the injured knee in comparison to the normal knee. When considering males as a group, four square millimeters of the cartilage of the ACL injured knee underwent significant thinning compared to the normal side, and this occurred in the medial superior aspect of the patellar, (mean thickness difference = -0.381 mm, with SD = 0.084mm). Analysis of the females as a group revealed that five square millimeters of cartilage of the ACL injured knee underwent significant thickening compared to the normal side, and this occurred in the medial inferior aspect of the patella (mean thickness difference = 0.551 mm, SD = 0.015mm). The findings from this study indicate that directional, regional and sex specific cartilage thickness changes occur following ACL injury, surgery, and 4 year follow-up